D.c. voltage regulator employing a zener diode



Dec. 8, 1970 J. M. MARZOLF 3,546,566

D.C. VOLTAGE REGULATOR EMPLOYING A ZENERDIODE Filed Nov. 27, 1968 1- lo I '7 l4 4. INPUT a OUTPUT u H IS I:

BY Mama ATTORNEY United States Patent O 3,546,566 D.C. VOLTAGE REGULATOR EMPLOYING A ZENER DIODE Joseph M. Marzolf, Falls Church, Va., assignor to the United States of America as represented by the Secretary of the Navy Filed Nov. 27, 1968, Ser. No. 779,408 Int. Cl. G05f 1/58 US. Cl. 323-9 2 Claims ABSTRACT OF THE DISCLOSURE A voltage regulator including a transistor which acts as a variable series impedance in response to a feedback signal generated by a circuit including a Zener diode, a voltage divider and a single additional transistor. The circuit inherently provides short-circuit overload protection for the components. Also, by adjustment of the-voltage divider, the regulated output voltage can be varied Without replacement of the Zener diode.

STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The invention relates generally to improvements in voltage regulators and the like, and more particularly, to a new and improved voltage regulator circuit having fewer parts than existing devices while permitting adjustment of the regulated output voltage without the necessity of replacing any components. Existing regulators have used Zener diodes as the basic regulating elements. Although such devices have served the purpose, they have not proved entirely satisfactory under all conditions of service for the reason that adjustment of the regulated output voltage could only be made by replacing the Zener diode with another having a different regulating point or by adding a voltage divider to the output of the circuit. Both of these approaches are cumbersome and costly, especially where the number of regulators used is high, and limit the ultimate capability of the design engineer.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide a voltage regulator which embraces all the advantages of similarly employed prior art devices, possesses none of the aforedescribed disadvantages, and uses fewer components to perform these functions.

More particularly, the circuit comprises a first transistor having its emitter-collector path connected in series between an input terminal and an output terminal. The collector-emitter path of a second transistor is connected in series with a first resistor between the base electrode of the first transistor and a common reference point. The base electrode of the second transistor is connected to the junction of a second and a third resistor coupled in series between the collector of the first transistor and the common reference point. A capacitor is connected between the input terminal and the base of the second transistor and a Zener diode has its cathode connected to the collector of the first transistor and its anode connected to the emitter of the second transistor to complete the circuit. Any change in the output regulated voltage varies the current through the Zener diode causing the second transistor current to thereby vary the impedance of the series interposed collector-emitter path of the first transistor thus maintaining a regulated output voltage. If the load Patented Dec. 8, 1970 current becomes excessive, the current through the Zener diode decreases and the voltage on the base of the sec ond transistor decreases thereby cutting off the current flow through the collector-emitter path of the second transistor which cuts off the collector-emitter path of the first transistor. Thus, any load up to and including a short circuit can be imposed upon the voltage regulator with no adverse effect.

Accordingly, it is one object of the present invention to provide an adjustable voltage regulator circuit.

A further object of the present invention is to provide an effective voltage regulator which uses only two transistor devices.

A still further object is to provide a voltage regulator circuit which is self-protecting against excessive load current.

BRIEF DESCRIPTION OF THE DRAWING Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing wherein:

The figure is a schematic circuit diagram of the preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, there is shown an input terminal 10 and a common reference line 11. The input terminal 10 is connected to the emitter electrode of transistor 12 and to one end of capacitor 13. The collector of transistor 12 is connected to output terminal 14 as well as to reference line 11 via the series network comprising fixed resistor 15 and variable resistor 16. The junction point of resistors 15 and 16 is connected to the other end of capacitor 13 as well as to the base electrode of transistor 17. The collector of transistor 17 is connected to the base of transistor 12. The emitter of transistor 17 is connected to common reference line 11 via resistor 18 and also to the anode of a Zener diode 19. The cathode of Zener diode 19 is connected to the output terminal 14 to complete the circuit.

The operation of the circuit will now be described. When an unregulated positive D.C. voltage is applied between the input terminal 10 and the reference line 11, current begins to flow through capacitor 13, the base-emitter diode of transistor 17, and resistor 18. This current causes current to flow from the input source through the base-emitter diode of transistor 12, the collector-emitter junction of transistor 17, and resistor 18 to reference line 11. This current flow consequently produces an initial conduction path through the emittercollector junction of transistor 12 to the output terminal 14. The capacitor 13, once it is fully charged, becomes an open circuit and has no further effect on the operation of the circuit. As the input voltage increases, the output voltage across the terminals 14 and 11, will follow the input voltage until the regulating point is reached. This point is determined by the breakdown value of Zener diode 19, the characteristics of transistor 17, and the relative values of resistors 15 and 16 which operate as a voltage divider to supply bias potential to the base of transistor 17. As the bias point of transistor 17 is selectively adjusted by resistor 16, the regulated output voltage of the circuit correspondingly changes, with the same Zener diode. As the input voltage increases further, the Zener diode will break down and begin to conduct current through resistor 18. This current will tend to cause transistor 17 to cut off at the point determined by the setting of variable resistor 16 with respect to resistor 15. As transistor 17 is driven further towards cut-off, the current flow through the emitter-base diode of transistor 12 will cause its emitter-collector impedance to increase so as to limit the output voltage. Thus, a constant output voltage appears across terminals 14 and 11 as the input fluctuates.

If a short circuit develops at the output of the device, the voltage across the series combination of resistors 15 and 16 becomes zero, causing the voltage at the base of transistor 17 to drop to zero. The short circuit also causes the Zener diode to open so that transistor 17 becomes cut ofi thereby blocking the current flow through the emitter-base diode of transistor 12 to drive it into a cut-off condition. Thus, a high current flow from the power source is prevented from destroying the series transistor 12, as Well as the rest of the components in the circuit.

In conclusion, there is provided a simple, reliable voltage regulator which effectively regulates the output voltage of a power supply, is protected against overload conditions, and provides an adjustable output voltage.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein in the light of the above teachings.

What is claimed and desired to be secured by Letters Patent is:

1. A regulator having an input terminal, an output terminal, and a common reference terminal, comprising:

a first transistor, having at least a first electrode,

a second electrode, and a third electrode, said first 3 electrode being coupled to said input terminal, and

a first resistor coupled between the first electrode of said second transistor and said common reference terminal;

a Zener diode having a cathode coupled to said output terminal, and an anode coupled to the first electrode of said second transistor;

a second resistor coupled between the second electrode of said first transistor and the third electrode of said second transistor; and

resistance means coupled between the third electrode of said secondtran'sistor 'and' saidcomrndn reference terminal;

whereby an unregulated DC. voltage signal having a magnitude greater than a predetermined value applied between said input terminal and said common reference terminal causes a constant DJC. voltage signal having said predetermined value to appear beween said output terminal at said common reference terminal.

2. The regulator of claim 1, wherein:

said resistance means is an adjustable resistor for varying said predetermined value within a range of values; and

said first, second and third electrodes of each of said first and second transistors are emitter, collector, and base electrodes, respectively.

References Cited UNITED STATES PATENTS 8/1965 Kuriger' 323 22 T 3,211,989 10/1965 Mintz et al. 323 22 (T) 3,419,789 12/1968 Gately 323-42 'r J D MILLER, Primary Examiner A. PELLINEN, Assistant Examiner 6 US. 01. X.R. 323 22, 3s 

